Effective motor control requires continuous monitoring and correction of errors. While it was originally postulated that errors are corrected using sensory feedback, the inherent delays render control inadequate and unstable. One solution is that the CNS implements a forward internal model (FIM) that predicts the sensory consequences of motor commands. The predictions are then compared to the actual sensory consequences, generating sensory prediction errors (SPEs) used to improve subsequent predictions. Extensive research suggests that the cerebellum serves as a FIM, but the mechanisms by which SPEs are encoded are unknown. The overall goal of this proposal is to understand the mechanisms of error encoding by the primary output neurons of the cerebellar cortex, Purkinje cells (PCs), as well as their projection targets in the deep cerebellar nuclei (DCN). While the dominant hypothesis is that errors are encoded by the low frequency PC complex spike (CS) discharge, results from our lab have implicated simple spike (SS) discharge in the processing of both prediction and feedback of performance error signals. Many PCs have this dual representation for both kinematics and performance errors, and the prediction and feedback signals have opposing effects on the SS, consistent with an SPE. Further, SS discharge related to performance errors is represented across a range of time scales (-2000 to 2000 ms), suggesting a potential relevance to working memory The first aim of this proposal seeks to investigate the nature of the dual encoding by observing how disrupting sensory information pertinent to motor error prediction and feedback modulates PC and DCN activity in order to test the hypothesis that the encoding represents the predictive and feedback components of an SPE. The second aim of this proposal seeks to investigate the role of SS discharge in encoding motor memories. A new tracking paradigm will be utilized requiring the encoding, maintenance, and retrieval of a simplified trajectory. The hypothesis is that aspects of the trajectory will be encoded by the SS discharge during each of the three stages of the paradigm. The results of this proposal will shed light on the cellular mechanisms behind error processing in the cerebellum relevant to both online motor control as well as motor memory.